Lichen Diversity
Lichens are classified as fungi and the fungal partners belong to the Ascomycota and Basidiomycota. Lichens can also
be grouped into types based on their morphology. There are three major types of lichens, although other types exist as
well. Lichens that are tightly attached to the substrate, giving them a crusty appearance, are calledcrustose lichens.
Those that have leaf-like lobes arefoliose lichens; they may only be attached at one point in the growth form, and
they also have a second cortex below the medulla. Finally,fruticose lichenshave rounded structures and an overall
branched appearance.Figure 5.39shows an example of each of the forms of lichens.
Figure 5.39 Examples of the three types of lichens are shown here. (a) This is a crustose lichen found mostly on
marine rocks,Caloplaca marina. (b) This is a foliose lichen,Flavoparmelia caperata. (c) This is a fruticose lichen,
Letharia vulpina, which is sufficiently poisonous that it was once used to make arrowheads. (credit b and credit c:
modification of work by Jason Hollinger)
What are the three growth forms of lichens?Resolution
Sarah’s mother asks the doctor what she should do if the cream prescribed for Sarah’s ringworm does not
work. The doctor explains that ringworm is a general term for a condition caused by multiple species. The
first step is to take a scraping for examination under the microscope, which the doctor has already done. He
explains that he has identified the infection as a fungus, and that the antifungal cream works against the most
common fungi associated with ringworm. However, the cream may not work against some species of fungus.
If the cream is not working after a couple of weeks, Sarah should come in for another visit, at which time the
doctor will take steps to identify the species of the fungus.
Positive identification of dermatophytes requires culturing. For this purpose, Sabouraud’s agar may be used. In
the case of Sarah’s infection, which cleared up within 2 weeks of treatment, the culture would have a granular
texture and would appear pale pink on top and red underneath. These features suggest that the fungus is
Trichophyton rubrum, a common cause of ringworm.
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224 Chapter 5 | The Eukaryotes of Microbiology
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